Internal combustion engine designs must cope with the increasingly stringent regulations on pollutant emission and fuel economy. One way to reduce emissions and increase fuel economy is to accurately control the combustion air/fuel ratio. This is generally accomplished by more precisely controlling the amount of fuel injected into an engine. U.S. Pat. No. 6,382,198 describes a direct injection engine with an enhanced fuel control system using a single oxygen sensor as combustion performance indicator. The Engine Control Module (ECM) of this system is capable of determining the actual air/fuel ratio corresponding to each individual cylinder. Such an ECM may be known as an Individual Cylinder Fuel Control (ICFC) module and is configured to develop individual correction factors for each individual fuel injector. However, it has been observed that many fuel injectors do not have fully predictable flow performances, which leads to performance deviation or variability between injectors of a same design. Variability between injectors is generally linked to production process variation and/or to the time-drift variations due to aging. Thus, individual fuel injector flow variations need to be corrected.